The present invention relates to a process and a device for uniform distribution of a free-flowing reaction mixture onto a continuously transported substrate over the desired width during production of foam webs. The distribution takes place by means of a stream of air.
The simplest method of applying a foamable reaction mixture to a moving substrate is to centrally feed the mixture onto the substrate, which is generally a paper web carried on the conveyor belt, and to allow the reaction mixture simply to run outwards. The paper web prevents the reaction mixture from adhering to the conveyor belt. Generally, the film of reaction mixture which forms is of uneven thickness. The differences in thickness are compensated somewhat during foaming; however, the cell structure of the resultant foam is generally not uniform.
Distribution rollers have therefore already been used. However, these can be employed economically only for the production of foam webs which have covering sheets on both sides to prevent the distribution rollers from contacting the reaction mixture. Since a bulge of reaction mixture must form in front of the distribution rollers, the residence times are relatively high.
For this reason, attempts have been made (German Offenlegungsschrift 1,778,951) to distribute the bulge more quickly towards the sides using jets of air issuing from blow nozzles, in order to shorten the residence time. However, this measure is also unsatisfactory, because the streams of air impinge almost perpendicularly on to the film of mixture and at the point of impingement drive the mixture almost completely towards the sides.
German Auslegeschrift 1,296,791 (corresponding to GB 1,031,753) discloses arranging an air chamber containing a porous plate over the width of the substrate, from which plate an airstream field issues countercurrently to the film of mixture. The degree of distribution is low when using such an air chamber, since there is no transversely distributing current.
The object of the present invention was to improve the distribution of the reaction mixture to thereby achieve a film of uniform thickness having a relatively short residence time.